Preheating apparatus for Diesel engines

Abstract

A parallel circuit of an ordinary resistor exhibiting an ordinary resistance characteristic and a starting resistor abruptly increasing its resistance at a certain temperature is inserted between glow plugs in a Diesel engine and a battery. The resistance of the starting resistor is smaller than that of the ordinary resistor at a normal temperature. The resistance of the starting resistor becomes larger than that of the ordinary resistor when a large amount of current flows through the starting resistor. Therefore, current flows from the battery to the glow plugs mainly through the starting resistor at first, and then it flows mainly through the ordinary resistor. A voltage drop of the battery due to engine starting is prevented by bypassing the parallel circuit by a resistor. Preferably, the starting resistor is of honeycomb shape.

We claim: 
     
       1. A preheating apparatus for Diesel engines comprising: a glow plug disposed in a cylinder-head of an engine;   starting resistor means connected between a voltage source and said glow plug, said starting resistor means including a resistance body principally composed of barium titanate to exhibit a resistance characteristic of a positive resistance temperature coefficient and abruptly increasing its resistance value at a predetermined temperature; and   ordinary resistor means connected in parallel with said starting resistor means;   said starting resistor means showing a resistance value smaller than that of said ordinary resistor means when a temperature of said glow plug is relatively low, and said starting resistor means showing a resistance value larger than that of said ordinary resistor means when the temperature of said glow plug is relatively high.   
     
     
       2. An apparatus according to claim 1, wherein said resistance material is substantially of honeycomb shape having a plurality of passages isolated from each other by a plurality of isolating walls each having an electrode film on its surface, and wherein said starting resistor means further includes: positive contact electrode means and negative contact electrode means for contacting with said electrode films so that each of said isolating walls is inserted between each of said positive and negative contact electrode means pairs, to thereby flow current through said walls in a direction perpendicular to the axes of said passages; and   a metallic case for covering said resistance material.   
     
     
       3. An apparatus according to claim 1, wherein said resistance material is of substantial plate shape, and wherein said starting resistor means further includes: positive and negative electrode means for sandwiching said resistance material; and   a metallic case for covering said resistance material.   
     
     
       4. An apparatus according to claim 1, 2 or 3, further comprising: switch means having a preheating contact position for supplying current from said voltage source to said glow plug through the parallel circuit of said starting resistor means and said ordinary resistor means, and a starting contact position; and   bypass means connected between the starting contact position and said glow plug, and including a resistor for adjusting a voltage across said glow plug, said bypass means supplying current from said voltage source to said glow plug through said voltage adjusting resistor during starting of said engine.